The present invention relates to electronic documents. The use of electronic documents is gaining popularity, and a variety of different formats of electronic documents exist that can be processed by different computer software applications. One example of a common, platform-independent type of electronic document is a PDF (Portable Document Format) document, which has been developed by Adobe Systems Incorporated, San Jose, Calif. PDF documents can be read by PDF readers, such as Adobe® Acrobat® and Adobe® Acrobat® Reader®, or other types of software applications.
While electronic documents are convenient in many ways, they also present a number of issues that may make it difficult to authenticate and/or trust the content of a document. One such issue is that an electronic document may contain state dependent content—that is, content that can be rendered to have a different appearance depending on, for example, when or in what environment the electronic document is viewed.
This makes it possible for malicious users to manipulate the electronic document, such that the document does not always reflect what the author of the electronic document originally created or what a user of the document sees. As a result, a user who takes action in reliance upon such a document may in fact be relying on a document whose content does not actually reflect his or her expectations.